In the recent move towards IP (Internet Protocol), it is considered, without exception, to introduce IP on voice communication systems, of which telephone networks are representative. In the 3GPP (3rd Generation Partnership Project) which is a standards organization associated with mobile communications, standardization of IMS (Internet Multimedia Subsystem) is being implemented as a basis for providing multimedia services such as voice services on IP networks. In recent years the 3GPP has been investigating the use of IP on fixed-lines known as NGN (Next Generation Network).
In today's electronic mail services, the behavior of senders sending mail unilaterally, against the wishes of receivers, which is called spam or junk mail, has become a social issue. As a background to this issue, reasons can be considered in that communication costs have dropped significantly accompanying the ubiquitous of the Internet, and that it is possible to send mass e-mails from a network access terminal such as a personal computer, which can be obtained easily.
It is considered that there is a high possibility that IMS will also get into a similar situation that today's e-mail service is in. A study of techniques for protecting users from this SPIT (spam over IP Telephony) has been started, called PUCI (Preventing against Unsolicited Communication for IMS), in the 3GPP field.
A technique is disclosed in Patent Document 1, which determines whether a call is SPIT or not using a blacklist.